Anatomy, pathophysiology, and biomechanics of shoulder instability.

Instability in the athlete presents a unique challenge to the orthopaedic surgeon. A spectrum of both static and dynamic pathophysiology, as well as gross and microscopic histopathology, contribute to this complex clinical continuum. Biomechanical studies of the shoulder and ligament cutting studies in recent years have generated a more precise understanding of the individual contributions of the various ligaments and capsular regions to shoulder instability. An understanding of the underlying pathology and accurate assessment of degree and direction of the instability by clinical examination and history are essential to developing appropriate treatment algorithms.